Pic 1 and 2 is bottom and top screw set, just let handle plate set at mid, leave enough space for valve open, but don't touch the bottom, so the valve will get all weight from plug, during the casting u should manage lead flow speed, less lead in pot lead will flow slower, turn valve plug to clean valve(push down then left right turn), then 1/8 turn to open up lead flow speed.
Pic 3 is another side of the homemade base
Prep pot, when it new, check the plug first, smooth it out if rough surfaces (the surface touching valve )